With the price of gasoline in the headlines each day and the political correctness of being "green", I thought I would write a short article about Oxygen Sensors.
Oxygen sensors adjust the air fuel ratio in a combustion engine by sending a specific voltage to the ECM(electronic control module). There are several other sensors that also send signals to the ECM. All of these sensors together control the emission control system. The ECM uses all of the information together to trim the air fuel ratio. The oxygen sensor is a key component of the system.
Oxygen sensors started coming out in American cars in the 1980s. The early versions of the oxygen sensors were quite simple and only had one wire which transmitted the voltage. These types are called unheated. Later versions had their own heaters, had three wires, and were called heated. In the early version the car had to warm up before the oxygen sensor could properly work. The later versions heat up almost immediately helping to get better gas mileage and less exhaust gases. There are some later models that have an even better oxygen sensor in them, but I am not going there in this article.
If the oxygen sensor fails your car will still run, but it will run inefficiently and cause increased fuel usage as well as exhaust emissions. The unheated versions usually last about 50,000 miles and the heated about 100,000 miles. Soot build up is the main cause of failure for an oxygen sensor. Because of this, often the second sensor does not last as long as the first. This is mostly because of wear and dirt in other parts of the engine.
I have read that a bad oxygen senor can cause as much as a 20% drop in mileage. I personally think the range is between 8 and 10%. It would mainly depend on your driving conditions and the condition of the vehicle. I have a 15 gallon tank and have to fill up about once a week. So a 10% increase would be about $6 a week or $300 a year savings. That is more than enough to pay for a new oxygen sensor if needed.
span style="font-family:verdana;">In almost all cars if the oxygen sensor fails, your engine light will come on, however in older cars the light may be burned out, or if you have purchased a used car from someone not so honest they may have disconnected this light. I have seen this done before. In fact it was done on the car I mention below. I suggest that anytime you have your car tuned up you make sure to ask to have the oxygen sensor tested. In newer cars this is quite simple because they can plug into the ECM and get a report back on the condition of the oxygen sensor. But, in the older cars the engine light comes on and the ECM just gives a signal that the oxygen sensor is bad. In the older cars the signal is not as reliable. I once had an oxygen sensor signal on a 1991 Mitsubishi that ended up being a bad ECM. If you are working on your own car a good car manual will advise you on how to check your sensor.
One more thing to add. I would also suggest that if you replace the oxygen sensor yourself, that you buy a brand name after market sensor. Don't buy the cheapest part offered. There are some good sensors from new companies out there, but there are also some that will appear and work good initially but, fail after 5000 to 7500 miles.The good companies will back their products with a good warranty.
Jeff Roberts
New Auto Accessories
